The present invention is directed to an improved load-handling clamp capable of handling two or more stacked loads of differing sizes, such as vertically-stacked abbreviated-height paper rolls of different diameters. Such a clamp is often referred to as a split-arm clamp. Preferably, the clamp is also useful for handling a single full-height or abbreviated-height load, or multiple stacked loads of the same size.
Such a split-arm clamp normally consists of at least a pair of separately-actuated clamp arms on one side of the clamp, in opposed relation to a single larger clamp arm on the opposite side of the clamp. The separately-actuated clamp arms are powered by separate hydraulic actuators connected in parallel to a source of pressurized fluid, and give the clamp the ability to apply clamping force separately to multiple objects of different widths or diameters stacked one atop the other. Such clamping capabilities are useful, for example, with respect to stacked paper rolls, bales or cartons of different sizes.
A common problem with such a clamp is misalignment of the separately-actuated clamp arms due to different frictional resistances in the respective arm mechanisms as they close or open, and/or different starting positions of the clamp arms when they close or open. If the clamp arms are misaligned to any extent, their combined profile will usually be thicker than normal. If the operator is unaware of such a misalignment, the clamp arms can strike a paper roll or other fragile load located inside the arms or adjacent loads located outside the arms as the arms are inserted or withdrawn in the course of engaging or depositing a load, causing substantial damage to the load. Correction of such misalignment often necessitates opening or closing the clamp arms to their maximum extent to realign them, which is time-consuming and requires operating space which may not be available.
A related problem is that, if only a single abbreviated-height paper roll or other single load is to be handled, clamping pressure on the load-engaging clamp arm cannot be obtained until the other separately-actuated arm is closed to its maximum extent. Conversely, opening of the clamp arms sometimes requires full opening of one clamp arm before another can be released sufficiently to disengage a load. In either case, the resultant high degree of misalignment of the clamp arms maximizes the time and space requirements for operating the clamp, and maximizes the risk of damage to the loads.
U.S. Pat. No. 4,682,931 offers a partial solution to these prior problems by providing a flow regulator of the divider/combiner type which requires the respective movements (or lack thereof) of a pair of clamp arms during closing and opening to be synchronized until the regulator is overridden, after which nonsimultaneous movement of the clamp arms is enabled. U.S. Pat. No. 5,984,617 improves on this system by making it compatible with clamp force adjustment systems. However, after the regulator has been overridden, the resultant unsynchronized arms must be opened or closed fully to resynchronize their positions, requiring extra time and space which may not be available.
Mechanical, rather than flow-regulating, solutions to the foregoing problems of unsynchronized clamp arms have been attempted in the past. These alternative solutions interconnect separately-actuated clamp arms by means of mechanical linkages which permit only a limited range of movement between the clamp arms. Such mechanical linkages include simple flexible or articulated tether-type links, or mechanical or hydraulic balance-beam links, which prevent more than a predetermined misalignment of the clamp arms. These linkages, however, share the common problem that they do not correct misalignment of the clamp arms and return them to their synchronized positions automatically to minimize their combined thickness.
Other previous linkage mechanisms include a spring-biased detent assembly tending to hold separately-actuated clamp arms in alignment with each other, but allowing large deviations from alignment whenever the spring-biased holding force of the detent is overcome by the fluid power actuators of the clamp arms. Such an arrangement provides neither adequate limitations on the misalignment of the clamp arms, nor automatic correction of such misalignment. Moreover, when only a single abbreviated-height load is to be handled, clamping pressure on the load-engaging clamp arm cannot be attained until the other clamp arm is fully closed.
A spring-link system shown in U.S. Pat. No. 6,318,949 is designed to cause synchronization automatically upon opening of the clamp arms. However the spring is limited in its ability to provide sufficient force to transfer hydraulic fluid rapidly enough to cause immediate realignment of the clamp arms. Moreover, such a spring link system can cause excessive mechanical limitations on visibility and the permitted extent of misalignment, depending on the particular profiles of the clamp arms. Also, clamping only a single load exerts the force of both fluid actuators into one clamping arm.